1. Field
Embodiments of the present invention generally relate to processing an ultra low-k dielectric film on a substrate with UV energy.
2. Description of the Related Art
Materials with low dielectric constants (low-k), such as silicon oxides (SiOx), silicon carbides (SiCx), and carbon doped silicon oxides (SiOCx), find extremely widespread use in the fabrication of semiconductor devices. Using low-k materials as the inter-metal and/or inter-layer dielectric between conductive interconnects reduces the delay in signal propagation due to capacitive effects. The lower the dielectric constant of the dielectric layer, the lower the capacitance of the dielectric and the lower the RC delay of the integrated circuit (IC).
Current efforts are focused on improving low-k dielectric materials, often referred to as ultra low-k (ULK) dielectrics, with k values less than 2.5 for the most advanced technology needs. Ultra low-k dielectric materials may be obtained by, for example, incorporating air voids within a low-k dielectric matrix, creating a porous dielectric material. Methods of fabricating porous dielectrics typically involve forming a “precursor film” containing two components: a porogen (typically an organic material such as a hydrocarbon) and a structure former or dielectric material (e.g., a silicon containing material). Once the precursor film is formed on the substrate, the porogen component can be removed using a thermal process, such as an ultraviolet (UV) curing process, leaving a structurally intact porous dielectric matrix or oxide network. The UV curing process also strengthens the film by cross-linking the matrix, e.g., Si—O—Si or Si—C—Si chains in the carbon doped silicon oxides, yielding a low-k film that is both mechanically and chemically stronger.
Techniques for removing porogens from the precursor film include, for example, a thermal process in which the substrate is heated to a temperature sufficient for the breakdown and vaporization of the organic porogen. One known thermal process for removing porogens from the precursor film includes a UV curing process to aid in the post treatment of CVD silicon oxide films. However, various exposed surfaces of the optical components, such as the quartz based vacuum window or showerhead disposed in the UV processing chamber, can become coated with organic-based residues (from a porogen precursor) that requires periodic cleaning. Overall, curing process throughput (number of substrates processed per hour) is determined by time needed for curing, cleaning and substrate transferring. Optimization of any of these steps increases UV process efficiency, which also increases overall device manufacturing efficiency.
Therefore, a need exists to increase UV efficiency while maintaining the film properties of deposited ultra low-k dielectric materials.